2D Viscous Hydraulic Design And Entropy Production Diagnosis Optimization Of An Ultra-low Specific Speed Centrifugal Pump

The ultra-low specific speed centrifugal pump has been widely applied in aerospace,petroleum,metallurgy and other industrial fields.However,its hydraulic design is lack of specialized theory and method.Therefore,based on the two dimensional?2D?flow theory,and aided by numerical simulation of the whole flow passage and experimental research,this dissertation has introduced turbulent boundary layer theory,entropy production diagnosis theory and orthogonal optimization to develop one newly theoretical model and numerical method,which is available for viscous hydraulic design and optimization of an ultra-low specific speed centrifugal pump.Firstly,the coordinate system of blade boundary layer has been established.Inside the boundary layer,the basic equations of relative flow are expanded.After magnitude analysis,simplification and integration,the momentum integral equation is obtained.This integral equation has kept effects of rotating centrifugal force,curvature centrifugal force and Coriolis force of the fluid inside impeller,which can consequently take into account influences of rotation effect and curvature effect on boundary layer development.Meanwhile,based on the Coles wake flow law,the mutual relationships have been built among boundary layer thickness,displacement thickness and momentum loss thickness.Then the numerical scheme of Range-Kutta is proposed to solve the integral equation above.Secondly,the 2D viscous hydraulic design method of the ultra-low specific speed centrifugal pump is proposed.In order to consider the effect of media viscosity on flow,the turbulent boundary layer theory is embedded into the 2D flow theory,and the displacement thickness obtained before is used to modify the exclusion factor.Based on the 2D inviscid and 2D viscous flow theories,the corresponding design codes have been developed separately.Then apply the two design programs to one IS single-stage single-suction ultra-low specific speed centrifugal pump,called reference pump.Two new pump models are obtained,called inviscid pump and viscous pump,respectively.The calculation results of the viscous pump indicate that along the direction of streamline,the turbulent boundary layer thickness grows slowly and then becomes fast,and it keeps increasing from shroud to hub.Additionally,the wrapping angle of the viscous pump is slightly larger than that of the inviscid pump.In order to investigate hydraulic performance of the newly designed pumps,the specialized hydraulic test platform has been set up.Combined with the experimental data,the numerical simulation method has been verified initially.Then based on the same numerical method,the hydraulic performance of the three pumps above are predicted.The results show that both the two newly designed pumps can meet the design requirements.Compared with the reference pump and at the design condition,the head and efficiency of the inviscid pump have been improved by 7.48%and 1.48%,respectively,and as for the viscous pump,those values are 5.41%and 2.49%separately.Furthermore,in order to quantitatively and intuitively investigate energy loss of the ultra-low specific speed centrifugal pump,the entropy production diagnosis theory is introduced.The entropy production formula of incompressible micro element is initially deduced,and then obtain the calculation models of direct entropy production,turbulence entropy production and wall entropy production.Using such theory,the entropy production performance of the pump is studied and got that the entropy production mainly generates in impeller and volute,while it is quite small in inlet and outlet pipes.The ratio of entropy production varies from 45.13%to 58.14%in the impeller and from 40.89%to 53.57%in the volute.The direct entropy production is quite small.The entropy production of the pump mainly are the wall entropy production and turbulent entropy production,and their proportions in the whole amount are58.71%⁶3.99%and 35.16%⁴0.43%,respectively.Combined with the analysis of internal flow field,the hydrodynamic mechanisms of entropy production have been attributed to the bad flow such as helical vortex,jet-wake and etc.Finally,based on the combination of the entropy production diagnosis theory and orthogonal experimental design,the optimization method of the viscous pump is put forward for the first time.The four geometrical parameters,including blade outlet setting angle ?₂,wrapping angle ?,volute inlet width b₃ and throat area S_t,have been selected to establish the orthogonal schemes.Then the range analysis based on entropy production minimization is made,and the best scheme is identified,namely ?₂=17°?b₃=12mm?S_t=200mm² and ?=210°.Lastly,the optimized pump is numerically calculated and the results indicates that after optimization,the numerical value and scale of entropy production is obviously smaller.Compared with the pump before optimization,the pump optimized realizes the further improvement of efficiency by1.08%in the premise of meeting the head requirement.